In an ink-jet printing system, a liquid ink is ejected from a nozzle towards a recording medium using a pressure, heat or an electric field as a driving source to print the recording medium. The ink-jet printing system can be used with a low running cost and form high quality images. Furthermore, this printing system can use various inks such as aqueous and oil-based inks. Accordingly, the ink-jet printing system has been expanding its market.
Under such circumstances, large-size ink jet printers, which can be used to print a sheet of the A-0 size with aqueous pigmented inks, have been developed, and are used to output indoor posters, CAD drawings, or proofing for color matching in printing. The printed materials can be used outdoors with laminating them.
Furthermore, the demand for outdoor use of the ink-jet printed materials has been increased. Therefore, there have been developed oil-based pigmented inks, which can be printed directly on films of polyvinyl chloride (hereinafter abbreviated to PVC) and used outdoors without lamination, and have excellent water resistance and weatherability.
Since the oil-based pigmented inks contains organic solvents as solvents, they do not cause the cockling of a paper sheet in comparison with aqueous pigmented inks, or require no lamination of a film having a receptive layer. Therefore, they can be printed on a substrate at low cost.
For example, there are proposed an oil-based pigmented ink comprising a glycol-based solvent having a boiling point of 150° C. or higher and a specific polyester resin (see Japanese Unexamined Patent Publication (Kokai) No. 7-109430 (pages 3 to 5)) and an oil-based pigmented ink comprising a glycol-based solvent having a boiling point of 200° C. or higher and a specific resin (see Japanese Unexamined Patent Publication (Kokai) No. 2002-302629 (pages 4 to 6)). However, when only a glycol-based solvent having a boiling point of 150° C. or higher is used, or a solvent having a boiling point of 200° C. or higher is used, the obtained ink has low drying property and has a problem that printed characters or images tend to blur when the ink is printed on a PVC film.
Also, oil-based pigmented inks containing 3-methoxy-3-methyl-butyl acetate as a primary solvent are proposed (see Japanese Unexamined Patent Publication (Kokai) No. 2004-231870 (pages 2 to 3) and Japanese Unexamined Patent Publication (Kokai) No. 2004-262985 (pages 2 to 3)). However, when 3-methoxy-3-methyl-butyl acetate is used as the primary solvent, the obtained ink has increased viscosity and is likely to cause ejection failure when the ink is printed using a printer comprising a head having a small nozzle inside diameter.